Circuit interrupter



March 1942- J. M. WALLACE CIRCUIT iNTERRUPTER Filed Dec; 28, 1939 ///KI///////// 7/////////// I// ii-.. 74 7// VII/Ill? INVENTOR James MWallace.

ATTOR WITNESSES:

rams Ma. 2 1942 2,277,619

UNITED. STATES PATENT- OFFICE.

CIRCUIT INTERRUPTER 'eames- M. Wallace, Braddock, Pa., assignor toWestinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., acorporation of Pennsylvania Application December 28, 1939, Serial No.311,358

17 Claims. (Cl. 200-413) My invention relates generally to circuitinterfuse which also embodies time lag protective rupting devices, andmore specifically to protecmeans, with anindicator or signal device toprotive interrupting devices which are adapted to vide a readily visibleindication of a circuit inautomatically interrupt an electric circuitupon terrupting operation; the passage therethrough of overload currentsof These and other objects of my invention will, predetermined values.become more apparent upon consideration of the In the protection ofelectrical circuits and apfollowing detailed description of preferredernparatus served thereby, it is desirable to protect bodiments thereof,taken in connection with the not only against relatively heavy overloadssuch attached drawing, in which: as short circuits, but also againstrelatively light Figure 1 is a longitudinal sectional view of aoverloads which may become harmful due to fuse embodying the features ofmy invention; their continued duration. Fig. 2 is a longitudinalsectional view of the Protection against these two types of overloadsupper end of the fuse shown in Fig. l and taken may be obtained by meansof a fuse wire which at right angles to the section of Fig. 1; embodiesa fusible connection of a low melting i5 3 3 is a e a y tud a sectionalpoint alloy as is disclosed in my copending apview of the upper end of afuse sim l r to Fi 1 plication, Serial No. 294,073, filed September 9,but showing a means for adjusting the spring 1939, and assigned to theassignee of this applicao ding on the bimetal element; tion. In thistype of protective device, the cir- Fig. 4 is a fragmentary longitudinalsectional cult is interrupted on light continuing overloads 2 v w of thepp d of a fuse sh wi another l in or through a mass of soft or moltenmetal, means for adjusti the Spring loading on t e the characteristicsof which may vary considere fll ent; ably, especially for varying massesof the metal. Fig. 5 is an end view of the fuse shown in Fig. The amountof metal is difficult to control, esd pecially for fuses of low currentratings where Fig. 6 is a fragmentary longitudinal e ti l small amountsare used view of a further modified form of fuse.

Accordingly, it is an object of my invention to In General, y novelinterrupt device inprovide a type of it interrupting. cludes afusiblelink connected between a pair of means capable of interrupting acircuit substan fuse terminals". with one of the connections intiailyinstantaneously upon the passage thereeluding ircuit opening meanscontrolled by a through of relatively heavy overloads, and which blmetelelement which may be heated y a sepawill also operate to open itscircuit inresponse to rate heating element y e Self-heated. A relativelylight but continuing ver10ads t spring is utilized to maintain thebimetal element time lag in engagement with the fuse link and, incertain Another object of my invention is to provide a forms f myinvention. I h ve provided means novel fuse embodying a fusible elementto sub- Wheieby the loading of h Spring may be manustantiallyinstantaneously interrupt a circuit upany altered t0 thereby y e rati gof the fuse. on the occurrence of relatively heavy overloads In theembodiment of y e tion shown in and short circuits, and which includesnovel Figs- 1 n 2, I have shown an elongated fuse means for interruptingthe circuit upon the octube 2 which may he of any Suitable insulatingcurrence of relatively light, but continuing overmaterial, such for p eas fi porcelain; l d V glass, or the like. The fuse tube 2 is providedIt is a further object of my invention t .v with end caps I and 6suitably secured over the vide a fuse incorporating a time lagprotective ends f the tube by the Screws 7- T nd n means, thecharacteristics of which are readily 5 is provided with a central iwardly punched manually adjustable to suit the particular cir- Opening 3receiving an dicating rivet memcuit requirements ber ill, the head ofwhich is shaped to be nor- It is a further object f my invention tprovide mally seated against the inclined sides of the a fuseincorporating a time lag protective means m n Opening An anchoringsleeve I2 is prowhich is automatically resettabla vided over the innerend of the indicating rivet Still another object of my invention is torol0 and includes an outwardly extending lower vide a fuse embodyingtime lag protective means flange 20, which serves as an abutment for onwhich is operable to open the circuit with a snapd of a l p ion Spring22' with the other action 1 end of the spring 22 being seated on theadja- Another object of my invention is to provide a cent end i the fusetube 2. The anchoring collar l2 also serves to anchor one end of a fuselink ll which includes a coil tension spring l6 having its lower endpassing through the anchoring sleeve '2 and bent over as at I4 tooverlie the flange 2! on the collar. The anchoring sleeve i2 may besecured to the indicating rivet ID in any desired manner, such forexample as by crimping or soldering.

The fuse tube 2 preferab1y'has a lining provided with a small bore toreceive the fuse link II, which lining is preferably of an insulating"provided by the reduced upper end of the fuse tube 2. The fusiblefilament 24 may be anchored to the insulating bar 26 as by being loopedaround the bar and then secured to itself as by soldering or the like,as shown.

Seated on the upper open end of the fuse tube 2 is a bimetal element 32.This bimetal element may be of any desired shape, such as of rectangularstrip form or spiral strip form and preferably so constructed as to bemovable with a snap action. However, it is herein illustrated as beingof concave disc shape so that the central portion thereof will engagethe portion of the fusible filament 24 which is wrapp d around theinsulating bar 26. The bimetal element 32 is composed of two metalliclaminations 34 and 24 intimately bonded together, for example as bywelding or the like, and which laminations are composed of materialshaving different coeflicients of expansion. The lamination I6 iscomposed of a material such as brass having a greater coemcient ofexpansion than the lamination 34 which may be of a material such asiron, so that when the bimetal element is heated, due to the unequalexpansion of the laminations, a force is built up to a value sufficientto suddenly reverse its curvature and attain a position corresponding tothe dotted line position. shown in Fig, l. Seated on. top of the bimetalelement- 32, I have provided a heating element 38 which may be of anysuitable resistance material, such for exam ple as carborundum orgraphite. The heating element 38 is provided with an integral reducedprojection 40 for telescoping into the lower end of a coil compressionspring 42 which has its other end seated in a recess 44 stamped in theupper fuse cap 4.

It can thus be seen that with the spring 42 normally held compressed,the circuit through the fuse will extend, for example, from the terminalcap 4 through the coil spring 42, heater 24, bimetal 32, fusiblefilament 24, coil tension spring i6, which is normally held 'in tension,indicating rivet member ill, to the lower fuse cap I. v

The manner of operation of this embodiment of my invention is asfollows: On the occurrence of relatively light continuing overloadcurrents, the current flowing through the heater 3! causes the bimetalelement 32 to becomeheated. When the temperature becomes high enough,the bimetal disc reverses its curvature and the circuit is openedbetween the disc and the fusible filament 24. In a high voltage circuit,this gap will be bridged by an arc. The are will burn the fusiblefilament wire in two, allowing the coil springs I8 and 22 to draw thefusible filament outwardly through the bore in the insulating blocks l9to thus draw out the are formed into contact with the gas evolvinginsulating material H to extinguish the arc. Due to the large mass ofthe heater 38 and the bimetallic element 32, the thermal capacity ofthese parts will be high and so the fuse will not operate on magnetizingsurges. It will, however, operate on currents which are far too small tocause fusion of the fusible wire 24.

Upon the occurrence of relatively heavy overloads, such as shortcircuits, for example, the fusible filament 24 will substantiallyinstantaneously be fused to interrupt the circuit in the same manner asbefore, before the heater 3! has a chance to heat the bimetal 32sufficiently to cause it to reverse its curvature. Obviously when thefuse operates to interrupt the circuit under any of the two precedingconditions, when the fusible filament 24 is broken, the coil compressionspring 22 is released and acts not only to aid spring it to draw out theare into engagement with the gas evolving insulating material I9, butalso acts to project the indicating rivet member 10 outwardly of the endcap 5 to a dotted line position such as is shown in Fig. 1. willobviously give a clear visible indication that the fuse is blown andneeds replacement.

On the occurrence of relatively light overloads in a low voltagecircuit, the gap introduced between the bimetal element 32 and thefusible filament 24 when the bimetal element quickly reverses itscurvature may be long enough to prevent an are from being sustained inthe gap. In this event, the fusible filament 24 is not destroyed and noindication is given by the indicating rivet III that the fuse is blown.However, this is not necessary since after the bimetal element 32 hascooled off it will reassume its normal position shown in Fig. 1 toreestablish the circuit through the fuse and thereby automaticallyre-establish the circuit.

The rating of the fuse will depend upon the loading of spring 42 whichasserts a force on the bimetal element 32 in opposition to its movementto open the circuit between the bimetal element and the fusible filament24. Thus, the rating of the fuse may be determined by the strength ofthe particular spring 42 which is employed.

In Fig. 3 I have shown a fuse wherein a single loading spring 42. may beemployed to obtain a fuse 'of various ratings. To accomplish thisresult, I have provided a threaded stud 46 extending through a centralaperture in the upper end fuse cap 4, and which is provided with anintegral lower inverted cup-shape portion 48 in which the upper end ofthe loading spring 42 may be seat ed. The stud 48 is threadedly engagedwith a nut 50 secured to the end cap 4 and may be locked in an adjustedposition by a cooperating lock nut 52.

It is believed obvious that by turning the stud 44 the loading on thebimetal element 32 may be changed, thus changing the force necessary toreverse the curvature of the bimetal element 32 which, in turn, changesthe amount of heat necessary to reverse the curvature of the bimetalelement 22, thus directly affecting the rating of the fuse.

If it is desired to provide a readily manually operable means forchanging the rating of my This load and low voltage conditions.

novel fuse. I have shown in Fig. 4 a construction wherein the loadingspring 4! has its upper end extending through a helical slot in a loadcontrol tube It which has a reduced upper .end portion 58 rotatablyreceived in a central aperture through the upper end cap 4, and anenlarged outer disc or dial portion which is accessible for manualoperation at the outer side of the fuse tube cap 4. As shown in Fig. 5,the dial it may be calibrated to provide a 2: 1 ratio of adjustmentofthe fuse rating.

The ability to easily manually vary the ratin of a fuse is especiallyadvantageous where close coordination with the capacity of the circuitor Y apparatus being protected is required, and also compensation forvarying ambient temperatures may be readily made in this fashion.

The bimetal element 32 may be self-heated if desired, thus eliminatingthe separate heater 38. In Fig. 6 I have shown such a structure wherethe heater element 3! of the previously described embodiments isreplaced by a block of insulating material 62 which serves as a seat forthe loading spring 42, and for insulating the spring from the bimetalelement. The outer edges of the bimetal element 32 are engaged beneath ashoulder 64 formed on the end cap 4. The circuit through the fuse inthis embodiment of my invention obviously extends from the fuse cap 4radially inwardly through the bimetal to the center thereof, thence tothe fuse link l8 and terminal cap 8 in the same manner described inconnection with the embodiment shown in Fig. l.

The operation of this form of my invention is identical with thatpreviously described in connection with that shown in Fig. 1 except thatthe bimetal is self-heating instead of requiring a separate heater.

It should be obvious from the foregoing, that I have provided a noveltype of circuit interrupting means which will give substantiallyinstantaneous protection against relatively heavy overloads on the orderof short circuits, which will give a time lag protection on relativelylight overloads, and which provides an automatically resettableprotective device under certain light Furthermore, I have provided afuse, the rating of which may be readily manually changed within a widerange.

Having described preferred embodiments of my invention in accordancewith the patent statutes,

I desire that it be understood that my invention is not limited to theparticular embodiments disclosed herein, inasmuch as it will be obvious,

particularly to persons skilled in the art, that many changes andmodifications may be made in these particular structures, withoutdeparting from the broad spirit and scope of my invention. Therefore, Idesire that my invention be interpreted as broadly as possible and thatit be limited'only by what is expressly set forth in the followingclaims.

I claim as my invention:

1. In av circuit interrupting device having a pair of' terminals, a fuselink connected to one of said terminals, and a thermally responsivemovable element connected to the other of said terminals and normallyengaging said link, whereby said element is movable away from said linkin response to predetermined conditions to break the. circuit, and thefusible portion of said link being closer to said element than otherconducting parts of the link at least when said element is moved awayfrom said link, whereby an 7 are will be established between saidelement and the fusible portion of said link.

2. In a circuit interrupting device having a pair of terminals, a fuselink connected to one of said terminals, and including a fusibleportion, and a thermally responsive movable element connected to theother of said terminals and having a part engaging the fusible portionof said fuse link, whereby said element is movable away from saidfusible portion in response to predetermined thermal conditions tostrike an arc to said fusible portion.

3. In a circuit interrupting device having a pair of terminals, a fuselink connected to one of said terminals, and means connecting said fuselink to the other of said terminals including a concavo-convexbimetallic disk movable to break the circuit adjacent said fuse linkwith a snap action in response to temperature changes.

4. In a circuit interrupting device having a pair of terminals, a fuselink having one end thereof connected to one of said terminals, and theother end thereof anchored to a support, means tensioning said fuselink, andthermally responsive means connected to said other terminal andhaving a movable part normally engaging said fuse link, and movable awayfrom said link in response to predetermined thermal conditions to inserta gap in the circuit.

5. In a circuit interrupting device having a pair of terminals, a fuselink and heating means connected between said terminals, and heatresponsive means for inserting a gap in the circult through the device,with said fusible element constituting one terminal of said gap inresponse to predetermined heating thereof by said heating means.

6. In a circuit interrupting device having a pair of terminals, a fuselink connected to one of said terminals, and a thermally responsivemovable element and electric heating means, in heating conductingrelation thereto connected in serial arrangement to the other of saidterminals, and said element having a part normally engaging saidfuselink.

7. In a circuit inter'ruting device, means for automaticallyinterrupting a circuit upon the passage therethrough of currents of apredetermined value, time lag means for automatically opening saidcircuit in response to the passage therethrough of currents of a lesserpredetermined value for a predetermined length of time, and said firstmentioned means being responsive to an are established by said time lagmeans to interrupt said circuit.

8. In a fuse, a fuse enclosure having a pair of spaced terminalportions, a fuse link in the tube having one end thereof anchoredrelative to the tube, said fuse link having the other end thereofconnected to one of said terminal portions, means for connecting saidlink to the other of said terminal portions including a part movableinto and out of engagement with said fuse link in response to thepresence or absence through the circuit of relatively light continuingoverload currents, and means tensioning said fuse link;

9. In a fuse, a fuse enclosure having a pair of spaced terminalportions,a fuse link in the enclosure having one end thereof anchored relative tosaid enclosure and having theother end thereof connected to one of saidterminal portions, means for connecting said link to the other of saidterminal portions including a bimetallic element having a part movableinto and out of engagement with said fuse link in response to thepresence or absence through the circuit of relatively light continuingoverload currents, and means tensloning said fuse link.

10. In a fuse, a fuse enclosure having a pair of spaced terminalportions. a fuse link in said enclosure having one end thereof anchoredrelative to said enclosure and having the other end thereof connected toone of said terminal portions, means for connecting said link to theother of said terminal portions including a bimetallic element having apart movable into and out of engagement with respect to said fuse link,and electric heating means in heat conducting relation with saidbimetallic element.

11. In a fuse, a fuse enclosure having a pair of spaced terminalportions, a fuse link in said enclosure having one end thereof anchoredrelative to said enclosure and having the other end thereof connected toone of said terminal portions, means for connecting said link to theother of said terminal portions including a bimetallic element having apart movable into and out of engagement with respect to said fuse link,electric heating means in heat conducting relation with said bimetallicelement, and resilient means for maintaining said heating means andbimetallic element in ensminent.

12. In a fuse, a fuse enclosure having a pair of spaced terminalportions, a fuse link in said enclosure having one end thereof anchoredrelative to said enclosure and having the other end thereof connected toone of said terminal portions, means for connecting said link to theother of said terminal portions including a bimetallic element having apart movable into and out of engagement with respect to said fuse link,electric heating means in heat conducting relation with said bimetallicelement, and manually adjustable resilient means for maintaining saidheating means and bimetallic element in engagement.

13. In afuse, fuse enclosure having a pair of spaced terminal portions,a fuse link in said enclosure having one end thereof anchored relativeto said enclosure and having the other end thereof connected to one ofsaid terminal portions, means for connecting said link to the other ofsaid terminal portions including a bimetallic element having a partmovable into and out of engagement with said fuse link in response tothe presence or absence through the circuit of relatively lightcontinuing overload currents, and means for varying the responsivenessof said movable part.

14. In a fuse, a fuse enclosure having a pair of spaced terminalportions, a fuse link in said enclosure having one end thereof anchoredrelative to said enclosure and having the other end thereof connected toone of said terminal portions, means for connecting said link to theother of said terminal portions including a bimetallic element having apart movable into and out of engagement with said fuse link in responseto the presence or absence through the circuit of relatively lightcontinuing overload currents, resilient means opposing disengagingmovement of said movable part, and manually operable means for varyingthe loading of said resilient means.

15. In a fuse, a fuse enclosure having a pair of spaced terminalportions, a fuse link in said enclosure having one end thereof anchoredrelative to said enclosure, said fuse link having the other end thereofconnected to one of said terminal portions, means for connecting saidlink to the other of said terminal portions including a part movableinto and out of engagement with said fuse link in response to thepresence or absence through the circuit of relatively light continuingoverload currents, means of a material capable of evolving an arcextinguishing gas when in proximity to an electric arc forming arestricted are passage in said tube, and means biasing said other end ofsaid fuse link for movement through said passage when said fuse blows.

16. In a fuse, a fuse enclosure having a pair of spaced terminalportions, a fuse link in said enclosure having one end thereof anchoredrelative to said enclosure, said fuse link having the other end thereofconnected to one of said terminal portions, means for connecting saidlink to the other of said terminal portions including a part movableinto and out of engagement with said fuse link in response to thepresence or absence through the circuit of relatively light continuingoverload currents, and indicating means responsive solely to rupture ofsaid fuse link for providing indication which is readily visible at theexterior of said fuse tube.

17. In a fuse, a fuse enclosure having apair of spaced terminalportions, a fuse link in said enclosure having one end thereof anchoredrelative to said enclosure, said fuse link having the other end thereofconnected to one of said terminal portions, means for connecting saidlink to the other of said terminal portions including a part movableinto and out of engagement with the fusible portion of said link to openand close the circuit in response to the presence or absence ofrelatively light continuing overload currents.

JAMES M. WALLACE.

